This invention relates to core drills used in drilling holes in concrete, hard fired brick and the like, and more particularly to provision of means attachable to a core drill for a drilling a pilot hole for the core drill.
The drilling of lengthy holes, e.g., holes 10-20 inches long, in structures or structural components made of concrete or other dense masonry materials is commonly accomplished with a core drill (also called xe2x80x9ccore drill bitxe2x80x9d) attached to a manually supported driver. A core drill commonly comprises an elongate hollow tubular member, one end of which is adapted to be releasably secured to the rotatable output shaft of a portable driver which typically is electrically powered but which may also be powered by a compressed gas such as air. Attached to the opposite end of the tubular member, usually by welding, is a tubular cutting head or bit that may comprise diamond or carbide particles embedded in a metal matrix. The core drill derives its name from the fact that as it drills into concrete or other dense material the interior of the drill fills with a solid core of the material that is being drilled. Typically water is injected into the core drill to facilitate the drilling process. When water is injected, the drilling process is identified as xe2x80x9cwet coringxe2x80x9d.
A problem with using core drills in hand-held drivers occurs when it is necessary to drill holes in concrete at precise locations. It is difficult to keep the core drill bit from wandering laterally when drilling is initiated, with the result that the resulting drilled hole may be not be centered at the desired location. Accordingly efforts have been made to provide means that aid in piloting the core drill so as to keep it centered on a predetermined point. One approach has been to (a) provide a template made of wood having a hole sized so that the core drill will make a close fit therein, (b) position the template against the concrete so that the hole is centered on the desired center point for the hole to be drilled in the concrete, (c) position the core drill in the hole in the template, and (d) operate the driver for the core drill so as to cause the latter to drill a hole in the concrete at the precise position exposed through the template. The template is discarded after the core drill has penetrated the concrete to provide a hole of limited depth, e.g., xc2xd to 1 inch, after which that hole serves as a pilot hole for the core drill, which is then used to extend the hole to a desired depth. However, that approach suffers from the limitation that two persons are required to form the pilot hole, one to hold the template and the other to hold the driver with the core drill. Another approach that has been considered is to drill a small pilot hole using a small diameter drill bit mounted in a light weight driver, and then, using different size drill bits in the same driver, enlarge that hole incrementally to the diameter of the hole which is to be drilled using a given core drill. Then the core drill is used to extend that hole to a selected final depth. As another approach, a special centering aid for core drills has been made and offered for sale by Hilti, a corporation having a place of business at 12330 E. 60th Street South, Tulsa, Okla. 74121 as its xe2x80x9cItem No. 00332495 Center Aid For Core Bitsxe2x80x9d. However, on information and belief, that device has not been commercially successful.
A primary object of this invention is to provide a method and apparatus for piloting a core drill as it drills a hole in concrete, fired brick or like material.
Another primary object of this invention is to provide a novel means of detachably securing a pilot tool to a core drill.
Another object of this invention is to provide a pilot tool assembly which is designed to fit within a core drill and to be locked to the core drill by a tight friction fit.
A further object is to provide a centering aid for a core drill that comprises a pilot tool unit that fits within the core drill, and expandable means interposed between the pilot tool unit and the core drill for releasably locking the pilot tool unit to the core drill.
Still another object is to provide a pilot tool assembly for a core drill that comprises means for providing a quick-release attachment to the core drill.
A more specific object is to provide a pilot tool assembly for a core drill which comprises a pilot tool unit that is sized to extend within the core drill and expandable means interposed between the pilot tool unit and the core drill and engagable with the interior surface of, the core drill for releasably locking the pilot tool unit to the core drill, the pilot tool assembly being removable from the core drill by application of an axial force to the pilot tool unit.
The foregoing objects are achieved by providing a pilot tool assembly that comprises a pilot tool unit that includes an elongate mandrel and a pilot tool secured to and projecting from one end of the mandrel. The pilot tool assembly also includes an expandable locking sleeve that surrounds and engages the outer surface of the mandrel. The mandrel is tapered so that its outside diameter increases with increasing distance from one end thereof, and the sleeve is made so that moving it relative to the mandrel in the direction of increasing mandrel diameter will cause the sleeve to expand radially. The pilot tool assembly is inserted into the drill bit end of the core drill so that the sleeve will engage the inner surface of the core drill, whereupon further axial movement of the pilot bit assembly into the core drill will cause the sleeve to move along the mandrel until it has expanded enough to frictionally secure the mandrel to the core drill, thereby making the pilot tool an auxiliary extension of the core drill so that it can be inserted in a predrilled pilot hole in concrete or the like and thereby serve to pilot the core drill as it is operated to drill a larger hole of limited depth. After the limited depth hole has been formed by the core drill, the pilot tool assembly is removed from the core drill and the latter is then used to extend the hole to a desired final depth. Removal of the pilot tool assembly is achieved by use of a push rod which forces the mandrel in a direction to release the grip exerted by the locking sleeve. In one specific embodiment of the invention, the pilot tool is a drill bit that may be used to form the predrilled pilot hole or to extend the length of the predrilled pilot hole as the core drill forms a larger diameter start hole coaxial with the pilot hole.
Other objects, features and advantages of the invention are described or rendered obvious by the following detailed description of a preferred embodiment of the invention which is to be considered together with the drawings identified below.